In-situ stress and wellbore stability of bohai oilfield in China

In order to reduce the frequently drilling accidents and complex level, increase drilling speed and reduce cost, we analyzed the in-situ stress and wellbore stability in Bohai Oilfield. Using geological mechanics method combining with Kaiser effect test and logging data we analyzed the direction of maximum horizontal in-situ stress and in-situ stress magnitude in Bohai Oilfield. Besides, experiments are conducted on formation mechanical characteristics of bedding shale in Shahejie Formation which is the most vulnerable formation occurring wellbore instability in Bohai Oilfield. According to the experiments a wellbore stability model in bedding shale was established. Then combining with the in-situ stress we analyzed the regular pattern of collapse pressure changing along with well track in bedding shale. The main reason for wellbore instability in bedding shale is that the bedding shale has a significant anisotropy and easily occur shear slip along the bedding plane. Combined with drilling practice we put forward engineering countermeasures for safety drilling in Bohai Oilfield. © 2013, EJGE.